This invention relates to semiconductor materials. More particularly, it is concerned with methods of epitaxially growing a semiconductor material on a substrate of the same or a different material.
In the fabrication of compound semiconductor devices and integrated circuits which include compound semiconductor devices, it is necessary to epitaxially grow layers of single crystal compound semiconductor materials directly on substrates of insulating and semiconducting materials. Metalorganic vapor phase epitaxy (MOVPE) techniques have been employed for this purpose.
The density of dislocations in the single crystal structure of III-V compound semiconductor materials is high compared to silicon. The dislocations are due to thermally induced stress while the bulk crystal is cooling from its growth temperature. These dislocations are present in wafers or substrates produced from the bulk crystal, and propagate in material epitaxially grown on the substrates. It has been even more difficult to obtain satisfactory device grade layers of III-V compound semiconductor materials grown on substrates of different materials, for example, silicon and sapphire. Although some techniques such as introducing strained layer superlattice structures have been employed to reduce the dislocation density in epitaxially grown III-V compound materials, additional complications are inherent with these structures.